KVM: SVM: Prepare for new bit definition in lbr_ctl

The lbr_ctl variable in the vmcb control area is used to enable or
disable Last Branch Record (LBR) virtualization. However, this is to be
done using only bit 0 of the variable. To correct this and to prepare
for a new feature, change the current usage to work only on a particular
bit.
Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/include/asm/svm.h

@@ -119,6 +119,8 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
 #define AVIC_ENABLE_SHIFT 31
 #define AVIC_ENABLE_MASK (1 << AVIC_ENABLE_SHIFT)
 
+#define LBR_CTL_ENABLE_MASK BIT_ULL(0)
+
 #define SVM_INTERRUPT_SHADOW_MASK 1
 
 #define SVM_IOIO_STR_SHIFT 2

arch/x86/kvm/svm.c

@@ -947,7 +947,7 @@ static void svm_enable_lbrv(struct vcpu_svm *svm)
 {
 	u32 *msrpm = svm->msrpm;
 
-	svm->vmcb->control.lbr_ctl = 1;
+	svm->vmcb->control.lbr_ctl |= LBR_CTL_ENABLE_MASK;
 	set_msr_interception(msrpm, MSR_IA32_LASTBRANCHFROMIP, 1, 1);
 	set_msr_interception(msrpm, MSR_IA32_LASTBRANCHTOIP, 1, 1);
 	set_msr_interception(msrpm, MSR_IA32_LASTINTFROMIP, 1, 1);
@@ -958,7 +958,7 @@ static void svm_disable_lbrv(struct vcpu_svm *svm)
 {
 	u32 *msrpm = svm->msrpm;
 
-	svm->vmcb->control.lbr_ctl = 0;
+	svm->vmcb->control.lbr_ctl &= ~LBR_CTL_ENABLE_MASK;
 	set_msr_interception(msrpm, MSR_IA32_LASTBRANCHFROMIP, 0, 0);
 	set_msr_interception(msrpm, MSR_IA32_LASTBRANCHTOIP, 0, 0);
 	set_msr_interception(msrpm, MSR_IA32_LASTINTFROMIP, 0, 0);